Device for starting an internal combustion engine, particularly a diesel engine

ABSTRACT

A method and a device for starting a diesel engine with no heater plugs, comprising pistons and cylinders defining combustion chambers into which gases intended to participate in combustion are admitted, in which method a strategy is adopted whereby the gases present in the chambers are heated up in such a way as to raise them to a minimum temperature within the entire volume defined by the chambers when the pistons are in the position of maximum compression or close to that position. The gases are heated by compressing the air in the cylinders using an electrical machine, or using a heating system in the intake.

The invention concerns the field of internal combustion engines,particularly automobile vehicle diesel engines.

It concerns more particularly a method and device for starting aninternal combustion engine including cylinders and pistons definingcombustion chambers into which are admitted gases intended toparticipate in combustion.

It is known that internal combustion engines are started by an electricstarter including a pinion adapted to mesh with a toothed ring gearconstrained to rotate with the crankshaft, i.e. the engine shaft. Theelectrical machine can also drive the crankshaft via a front face belt.

Engine designers are seeking to reduce the compression ratio of dieselengines in order to respond to increasingly severe antipollutionstandards.

Moreover, starter devices of this type cause a number of problems withregard to starting an engine, particularly a diesel engine, in coldweather, especially when the temperature is less than or equal to −25°C.

It is known to provide preheating by means of a plurality of glowplugs(one in each combustion chamber) fixed to the cylinder head of theengine. These glowplugs generate a hot spot in the combustion chamber,which enables combustion of the injected diesel fuel, even at very lowtemperatures.

However, the system using glowplugs for preheating is localised andleads to an increase in fuel consumption on starting and to an increasein polluting emissions because combustion is incomplete and is nothomogeneous. Moreover, the design of the cylinder head of the engine iscompromised by the presence of the glowplugs, which occupy a large spaceand interfere with the circulation of gases inside the combustionchamber. The glowplugs are also costly.

Furthermore, after a cold start using glowplugs, the internal combustionengine tends to be very unstable when idling, which leads to a number ofproblems such as vibration, noise, etc. In some cases, the engine caneventually stall.

Moreover, present day starter systems cannot achieve drive speedscompatible with a low compression ratio.

The invention proposes a high-performance system for starting dieselengines with a low compression ratio.

It aims in particular to provide a method and a device for starting aninternal combustion engine in cold weather, particularly at temperaturesless than or equal to −25° C.

A further object of the invention is to provide a starting method anddevice of this kind that do not necessitate glowplugs in the combustionchambers. To this end the invention proposes a method of the typedefined in the introduction in which a strategy is adopted whereby thegases present in the chambers are heated to a minimum temperaturethroughout the volume defined by the chambers when the pistons are inthe maximum compression position or near it, notably within plus orminus 10° of it.

It has been observed that obtaining a certain temperature level, notablyof around 415° C., substantially throughout the chamber enables reliablestarting, including starting under difficult conditions. Moreover, thereduction in the compression ratio must be accompanied by an increase inthe driving speed during the starting phase in order for the gases toreach the temperature necessary for self-ignition of the gases.

In a first embodiment, an electrical machine, notably an electricstarter, is coupled to the crankshaft of the engine to drive it inrotation at a chosen rotation speed that is higher than a normalrotation speed and is obtained by said electrical machine in order toincrease the compression of the air admitted into the cylinders of theengine and consequently the temperature in the cylinders. It is knownthat filling efficiency increases as the engine speed rises, to anoptimum value around the maximum torque engine speed, and then decreasesuntil the maximum engine speed is reached. This increase in compressionlinked to the increase in speed is explained among other things by areduction in the rates of leakage between the pistons and the cylindersand by reduced heat exchanges between the (hot) gases contained in thecombustion chamber and the (cold) walls of that chamber, and likewise aquantity of air introduced into the upper cylinder linked to an increasein the filling efficiency as the engine speed rises. This increase inthe quantity of air admitted further produces an engine torque that ishigher during starting, to overcome friction. This is because the workproduced by the increase in pressure linked to combustion is directlylinked to the quantity of fuel and air participating in combustion.There will therefore be an acceleration of the higher engine speedduring starting linked to this additional work produced on eachcombustion cycle.

While the average rotation speed of a crankshaft driven by an electricstarter at −25° C. is generally 110 revolutions per minute, theinvention proposes to operate the electric starter at a higher rotationspeed. This results in greater compression of the air despite a lowerengine compression ratio and in operating conditions favourable tostarting in cold weather, in any event to temperatures of the order of−25° C., because the quantity of air admitted into the cylinders of theengine is increased, thereby increasing the temperature in thecylinders. This is because the increase in the rotation speed of theelectric starter, and thus of the crankshaft, is reflected in anincrease in the linear speed of the pistons in the respective cylinders,leading to a reduction in leakage between the pistons and the cylindersand to reduced heat loss to the walls. The amount of leakage isproportional to the leakage time, and because the duration of thecompression/expansion phase decreases as the engine speed increases, theamount of leakage likewise decreases.

The rotation speed chosen is advantageously greater than 200 revolutionsper minute and more preferably greater than 300 revolutions per minute.

It is also possible to change the reduction ratio between the rotor ofthe electric starter and the crankshaft in order to increase therotation speed of the engine, in particular to a reduction ratio lessthan 40:1.

A gear starter has between the armature shaft and the starter pinion aninternal reduction gear stage the reduction ratio of which is around 3:1and in all cases less than 4:1, ideally less than or equal to 3.84:1.

The engine ring gear preferably has a number of teeth less than or equalto 100.

The compression ratio of the engine is advantageously less than 16.5:1.At present the compression ratio for a diesel engine is approximately17-18:1.

In another embodiment, the chambers being fed with gas intended toparticipate in combustion via a common pipe, said gases are preheatedwhile flowing in said pipe, particularly during starting. This canreduce the starting time.

In this embodiment, said gases can be preheated and their flowrateadjusted simultaneously.

By combining the foregoing two embodiments the gases intended toparticipate in combustion can be preheated and said electrical machineoperated at said chosen rotation speed in a coordinated manner.

More particularly, said gases can be preheated before operating saidelectrical machine at said chosen rotation speed.

This being the case, starting conditions can be detected and informationdeduced therefrom indicating a “cold start” or a “normal start”, andsaid strategy adopted depending on the starting conditions detected.

More particularly, the electrical machine can be actuated at the chosenspeed or at the normal speed, respectively in the case of “cold start”conditions or “normal start” conditions.

The starting conditions relate, for example, to a temperature difference(DT=TH−T or DT=TE−T) between the temperature (TE) of the engine coolingwater or the temperature (TH) of the engine lubricating oil and thetemperature (T) of the outside air (ambient temperature), defining “coldstart” conditions or “normal start” conditions according to whether thistemperature difference (DT) is respectively less than or greater than agiven threshold value (S), in particular 5° C., and the outsidetemperature (T) is respectively less than or greater than another giventhreshold value (S′), in particular 0° C.

The invention further concerns a starter device of the type defined inthe introduction including means for heating the gases present in thechambers to a minimum temperature throughout the volume of the chamberswhen the pistons are in the maximum compression position or near it,notably within plus or minus 10° of it.

In a first embodiment, said preheating means consist of an electricalmachine adapted to drive the crankshaft of the engine at a chosenrotation speed that is higher than a normal rotation speed obtained bysaid electrical machine in order to increase the compression of the airand the quantity of air admitted into the cylinders of the engine andconsequently the temperature in the cylinders.

The invention envisages in particular using a standard electric starter,i.e. a starter able to operate at a given electrical voltage, forexample 12 volts.

The resisting torque of the engine remaining substantially the same,increasing the power of the starter system in order to be able toincrease the speed at which the engine is driven must be envisaged.

Present day starter systems may not be able to achieve sufficientdriving speeds to start an engine with a low compression ratio. There isthen provision for connecting the electric starter to an electricalcircuit adapted to supply power to the starter at a boosted electricalvoltage, i.e. a voltage higher than the given electrical voltageconstituting the usual operating voltage of the starter.

The electrical circuit advantageously includes a primary voltage sourceadapted to deliver a nominal voltage of chosen value and a boostedvoltage source adapted to deliver a voltage higher than the nominalvoltage of the primary voltage source.

In a first variant, the boosted voltage source is a battery.

In one embodiment, the primary voltage source is a first battery adaptedto deliver a nominal voltage of 12 volts and the boosted voltage sourceis a second battery adapted to deliver a nominal voltage of 24 volts. Inthis example, the 24 V boosted voltage source can advantageously beproduced by connecting in series the first 12 V battery with a second 12V battery with substantially identical characteristics.

In a second variant, the boosted voltage source is a supercapacitor,i.e. a double-layer capacitor, or an ultracapacitor.

In one embodiment, the primary voltage source is a first battery adaptedto deliver a nominal voltage of 12 volts and the supercapacitor isadapted to deliver a voltage higher than 12 volts.

According to another feature of the invention, the electrical circuitincludes a DC-DC converter for charging the boosted voltage source fromthe primary voltage source. This converter can be reversible or not.

The electrical circuit can also include an electrical relay adapted tooperate the starter from the boosted voltage so

According to one variant, said circuit includes a first voltage sourcefor delivering said nominal voltage, a second voltage source andswitching means for combining said voltage sources to obtain saidboosted voltage.

Thus two batteries can be used, for example of the same voltage, and aswitching system for connecting said batteries in series or in parallelor for loading either both batteries or only one of them, depending onwhat is required.

It is desirable to have a value less than or equal to 4 mΩ for the sumof the internal resistances of the battery and that of the cable thatsupplies power to the electrical machine or the sum of the equivalentinternal resistances of all the batteries that participate in supplyingpower to the electrical machine during starting and that of all theircables. This can be achieved by using a large battery or cables of largesection.

Such a configuration is particularly suitable if starting conditions areidentified by comparing T and TE or TH, as indicated above.

A battery could be used with a supercapacitor adapted to be connected inseries with the battery.

The circuit could include a single battery for producing said nominalvoltage and a DC-DC converter for producing said boosted voltage,notably an electronic chopper/booster device between the battery and thestarter.

To facilitate starting, the starter control unit modifies theconnections of the different batteries and/or the supercapacitor of saidstarter according to two distinct phases during starting as such: afirst phase at a given voltage, and a second phase at a voltage higherthan that of the first phase. This solution reduces power consumptionduring starting because the battery is discharged less than when thevoltage delivered is constant throughout starting. It also has theadvantage of allowing more starting attempts and therefore a greaterchance of success under difficult conditions. Supercapacitors are ableto deliver a high electrical power but, given their size, cannot containmuch energy. In this solution of starting in two phases at twosuccessive voltages, a supercapacitor of reduced size, for example 300farads, is sufficient to assure the final phase of starting, in which ahigh speed is required to achieve the combustion temperature required inthe combustion chambers, but only for a relatively short time, forexample 1 to 3 revolutions of the crankshaft. When the temperature ofthe engine is low (less than 0° C. and even more so less than −20° C.),the pressure rise time of the injection rail is high. At suchtemperatures, the lubricating oil of the engine performs less well thanwhen the engine is warm (water temperature approximately 80° C.). Thiscauses an increase in the resisting torque of the engine. The startersystem therefore drives the engine more slowly at low temperature thanwhen the engine is warm. In many cases, the pump for pressurising theinjection rail is driven by a mechanical system linked to the crankshaftof the engine (belt, chain, gear train, etc.). The rotation speed beingproportional to that of the crankshaft, the pressure inside theinjection rail therefore increases more slowly during starting at lowtemperature, the effect of which is to lengthen the starting time.Paradoxically, it is indispensable to be able to drive the engine asquickly as possible in order to reheat the gases in the combustionchamber sufficiently to produce combustion of the mixture and start theengine. In the end, power consumption during starting is very highbecause, during the first moments, in which the starter is driving theengine, the pressure in the injection rail is too low to be able toinject the minimum quantity of fuel required to cause an explosion of anintensity adapted to start the engine.

Another object of the present invention is to reduce the electricalpower consumed by the starter system at the beginning of the phase ofdriving the engine and for as long as the pressure in the rail is toolow. When a sufficiently high pressure is reached, the starting systemis supplied with more power, enabling a very high rotation speed of thecrankshaft to be achieved. This high speed leads to fast heating of thegases in the combustion chamber and thus to starting in a very shorttime.

The change between the first phase and the second phase is effected whenthe pressure in the injection manifold exceeds a threshold sufficient toenable first combustion in one of the cylinders in order to supportstarting. This conserves power at the beginning of starting, when therotation speed is still low, to use it when the rotation speed rises,thus saving energy.

If starting is delayed, the change between the first phase and thesecond phase is effected when the duration of the first phase exceeds acertain time. This system is simple and enables starting without itbeing necessary to know the pressure in the injection manifold.

The duration of the first phase is a function of the outside temperatureand/or the temperature of the engine cooling liquid. If that temperatureis less than or equal to −20° the duration of the first phase is greaterthan or equal to one second.

If the starter machine is a gear starter driving an engine ring gear,the change between the first phase and the second phase is effected whenthe teeth of the starter pinion have begun partial or complete axialpenetration into the teeth of the ring gear. This avoids milling of thering gear.

In a different embodiment, the starter device instead or additionallyincludes preheating means that are adapted to preheat the inlet air andtherefore the gases intended for combustion and are provided in theinlet system of the engine in a pipe feeding all the combustion chamberssimultaneously.

In this embodiment, the preheating means include, for example, at leastone electrically resistive element (R) which can be integrated into avalve incorporated in said pipe for adjusting the flowrate of the gasesintended to participate in combustion.

Control means can then be provided for operating the preheating meansand the electric starter in a coordinated manner. These control meansare preferably adapted to operate the preheating means before theelectric starter.

In one embodiment, the starter device includes detector means adapted todetect starting conditions and to deduce therefrom informationindicating a “cold start” or a “normal start” and selector meansconnected to the detector means to actuate the electric starterrespectively at the chosen speed or at the normal speed.

In other words, the device of the invention can start the engine in twodifferent operating modes depending on the starting conditions detected.

The following description, which is given by way of example only, refersto the appended drawings, in which:

FIG. 1 is a diagram that represents an internal combustion engine withsome of its standard ancillary equipment, the engine being equipped witha starter device of the invention;

FIG. 2 represents the electrical circuit diagram of a first variant ofan electrical circuit for actuating the electric starter;

FIG. 3 is analogous to FIG. 2 for a second variant of the electricalcircuit;

FIG. 4 is analogous to FIG. 1 for a different embodiment;

FIG. 5 is a flowchart of the operation of the control means of the FIG.4 embodiment of the starter device;

FIG. 6 represents the three-phase starting cycle;

FIG. 7 is a flowchart of the operation of the control meanscorresponding to the three-phase starting cycle shown in FIG. 6;

FIG. 8 is a flowchart of the operation of the control means of thedevice corresponding to a variant of the three-phase starting cycleshown in FIG. 6.

Refer first to FIG. 1, which shows an internal combustion engine 10, forexample an automobile vehicle diesel engine, including an inlet manifold12 adapted to admit a flow of inlet air A into the combustion chambers(not shown) of the engine from an inlet pipe 14. The manifold 12 and thepipe 14 together constitute the inlet system of the engine.

The engine 10 is cooled by a cooling liquid flowing in a coolingradiator 16. The engine 10 includes a crankshaft (or engine shaft) 18 towhich a toothed ring gear 20 is keyed. In a manner known in the art, theengine is started by means of an electric starter 22 including a DCmotor driving a toothed pinion 24 adapted to mesh with the toothed ringgear 20 upon axial displacement of the pinion. The electric starter 22is a standard starter which, in this example, is designed to be drivenby a voltage source of the usual kind, such as a battery delivering anominal DC voltage of 12 volts.

According to the invention, the electric starter 22 is operated by meansto be described later to drive the crankshaft 18 at a chosen rotationspeed higher than the normal rotation speed. This chosen rotation speedis greater than 200 revolutions per minute in this example andpreferably greater than 300 revolutions per minute, whereas the normalrotation speed achieved by the starter in cold weather is usually 110revolutions per minute.

To this end, control means 26 (represented diagrammatically) operate theelectric starter 22 at this chosen rotation speed via an electricalcircuit 28 to be described later.

As indicated above, driving the crankshaft 18 at a higher rotation speedincreases the compression of the admitted air and the quantity of airadmitted into the cylinders of the engine and consequently thetemperature in the cylinders, which makes it easier to start the enginein cold weather.

To make starting easier, it is advantageous also or instead to provide,as shown in FIG. 1, preheating means 30 adapted to preheat the inlet airA. These preheating means advantageously include an electricallyresistive element R. Here they are disposed on the upstream side of theinlet manifold 12 of the engine, i.e. on the inlet pipe 14. Otherlocations are possible, for example at the entry of the inletdistributor of the engine or at the air inlet of each combustion chamberof the engine.

The control means 26 operate the preheating means 30 and the electricstarter 22 in a coordinated manner. These means 26 and 30 can beoperated simultaneously, but are preferably operated with a time shift.It is advantageous for the control means to operate the preheating means30 before they operate the electric starter 22, for example at the timeof an instruction to unlock the doors of the vehicle whose engine is tobe started.

Because of this, the standard preheating system using glowplugs in thecombustion chambers of the cylinders can be dispensed with. This resultsin a simplification of the cylinder head of the engine. Note, moreover,that the preheating system 30 is no more demanding of electrical powerthan a standard preheating system using glowplugs.

Refer next to FIG. 2, which shows one embodiment of an electricalcircuit associated with the electric starter of the invention. Theelectric starter 22, represented diagrammatically here by a dashedoutline rectangle, includes, in a manner that is known in the art, adirect current motor 32, a contactor 34, a pull-in winding 36 and ahold-in winding 38. The pull-in winding 36 causes the contactor 34 topick up while the hold-in winding 38 holds the contactor in the closedstate.

The electric starter 22 is connected to the electrical circuit 28mentioned above, which includes a circuit 40 incorporating a primaryvoltage source 42 and a boosted voltage source 44. In this example, thesource 42 is a first battery adapted to deliver a nominal DC voltage of12 volts and the boosted voltage source 44 is a second battery adaptedto deliver a nominal DC voltage of 24 volts. The 24 V boosted voltagesource can also be produced by connecting the first 12 V battery inseries with a second 12 V battery having substantially identicalcharacteristics.

The circuit 28 includes a starter contactor 46 adapted to be actuated byan ignition key or a contact card to start the engine. The contactor 46is supplied with power by the source 42, and therefore at a voltage of12 volts in this example. An electrical relay 48 is included in thecircuit 28 after the contactor 46 so that the starter can be operatedfrom the boosted voltage source 44, i.e. here at 24 volts.

Accordingly, at the time of a start request, closure of the startercontactor 46 operates the relay 48 which in turn operates the starterfrom the boosted voltage source 44, i.e. at 24 volts. The circuit 28thus supplies the electric starter 22 with power at a voltage higherthan the usual voltage, enabling it to assume a higher rotation speed,as already explained.

The boosted voltage source 44 can be replaced by means other than a24-volt battery, provided that such means are able to deliver a voltagehigher than the nominal voltage of the primary source 42. Thus in onevariant a supercapacitor can be used, i.e. a double-layer capacitor. Itis known that these capacitors have a much greater active area thanconventional capacitors, resulting in very high capacitance values.These supercapacitors also have the advantage of charging much fasterthan the usual batteries and of supplying a current of very high power.

Refer now to FIG. 3, which shows a variant of the circuit from FIG. 2.The difference here lies in the fact that the electrical circuit 40further includes a DC-DC type converter 50 for charging the boostedvoltage source 44 from the primary voltage source 42. This converter 50is inserted between two branches of the circuit 40 that respectivelyinclude the voltage sources 42 and 44. This applies regardless of thetype of boosted voltage source 44 used (battery, supercapacitor, etc.).

Refer now to FIG. 4, which shows a variant of the engine and itsenvironment shown in FIG. 1. Here the main difference lies in the factthat the control means 26 are connected to detector means for detectingthe starting conditions. More particularly, these detector means includea temperature sensor 53 for sensing the temperature of the air externalto the vehicle, a temperature sensor 52 for sensing the temperature (TE)of the engine cooling water or a temperature sensor 54 for sensing thetemperature (TH) of the engine lubricating oil. As explained later, itis thus possible to define different starting conditions, namely “coldstart” conditions and “normal start” conditions, depending on thedifference between the values T and TE or TH measured in this way.

Refer now to FIG. 5, which is a flowchart for the FIG. 4 embodiment. Thesensors 52 and 54 are connected to a computer 56 which computes thetemperature difference DT=T−TE or DT=T−TH. This computer is connected toa comparator 58 that compares the value DT to a threshold value S, forexample of 5° C., and determines whether T is less than a thresholdvalue S′, for example of 0° C. Two situations can then arise: if thevalue DT is less than the threshold value S and T is less than thethreshold value S′, it is deduced that the cold starting conditionsapply. On the other hand, if the value DT is greater than the thresholdvalue S or T is greater than the threshold value S′, it is deduced thatnormal starting conditions apply.

Thus the comparator 58 constitutes selector means which, depending onthe value of DT relative to S, command either a cold start or specialstart 60 or a normal start 62. In the case of a cold start 60, thecontrol means operate the electric starter 22 via the electrical circuit28 and the heating means 30 in a coordinated manner, as explained above.

In the case of a normal start 62, the control means 26 operate theelectric starter 22 under the usual conditions, i.e. the starter issupplied with power at the nominal voltage of the primary voltage source42. In other words, in this latter situation, the speed at which thecrankshaft is driven corresponds to the usual conditions.

FIG. 6 shows the interaction of the various elements with each other,the first curve at the top representing the power supply voltage of thestarter and the air preheater over time, the second curve in the middleshowing the pressure in the injection rail over time, and the bottomcurve showing in solid line the speed of the engine and in dashed linethe speed of the starter.

During a phase 0, the air is preheated, during the first phase (phase 1)the starter is supplied with power at a voltage T1 (I), the voltage thenchanges to T2 (II) during the second phase (phase 2), the voltagereturns to zero (IV) when the engine has started (III), the starter isdisconnected and stops rotating (V).

The voltages T1 and T2 are substantially constant, but a slightcontinuous fall in T and/or T2 can occur during starting because thebattery is gradually discharged.

The starting strategy can be different, depending on the circumstances:if the engine is started in cold weather, the voltage increases from T1to T2, with T2≧T1, whereas if the engine is warm (water or oiltemperature above a threshold, for example 50° C.) it is started in thestandard way with a substantially constant power supply voltagesubstantially equal to 12 V.

If the vehicle is equipped with a “stop and start” system, whichautomatically stops the engine when the vehicle is stationary, startingat the command of the driver with the ignition key or the start buttonis effected at voltages T1 and T2, whereas automatic restarting iseffected either at a substantially constant voltage or at voltages T1and T2, with the duration of the preheating phase 0 and the duration ofphase 1 at the voltage T1 depending on the conditions defined in theflowcharts of FIGS. 7 and 8.

The mode of operation of the control means of the two-stage starterdevice of the invention is described next.

First of all (phase 0), the air is preheated at a power supply voltageT1 for a duration that is determined depending on the temperature of theengine water or oil (first step in FIGS. 7 and 8). The duration of phase1 (second step in FIGS. 7 and 8) during which the starter is operatedand preheating is active at a voltage T1 is adjusted by an electroniccontrol system, optionally included in the computer, in two differentmodes.

In the first mode, represented in FIG. 7, the duration t1 for whichpower is supplied is predetermined depending on the temperature of theengine water or oil (longer when the engine is cold) or the temperatureof the outside air (longer when the outside temperature is lower). Forexample, for an outside air temperature equal to 20° C., the value of t1can be set at approximately 0.2 seconds and the value of t2 atapproximately 3 seconds, while for an outside air temperature equal to−25° C., the value of t1 can be set at approximately 1.5 seconds and thevalue of t2 at approximately 10 seconds.

In the second mode, represented in FIG. 8, phase 1 lasts until thepressure in the injection manifold has reached a pressure P1 that is theminimum pressure at which fuel can be injected into the cylindersconcerned to produce an explosion in said cylinders of sufficientintensity to start the engine. The order of magnitude of P1 is from 50%to 80% of P2, which is the pressure set point under stable idlingconditions. For example, if P2 is equal to 30 MPa, P1 will be equal to20 MPa. If the pressure P1 has not been reached after a predeterminedtime t′1, for example of 10 s, then the supply of power to the heaterand the starter is cut off.

At the end of this phase 1, the subsequent phases are identical for boththe FIG. 7 and FIG. 8 modes. In phase 2, the power supply voltage isincreased to T2 in order to reach a particularly high crankshaftrotation speed. The start of this phase 2 substantially corresponds tothe start of injection of fuel into the cylinders. As soon as thecrankshaft speed measuring means detect that the engine has started, thesupply of power to the starter is cut off, although that to the heatercan be continued, for example for a time of the order of 10 seconds to10 minutes, in order to stabilise the idling speed. If starting of theengine has not been detected after a time t2 of 5 s, for example, thestarter and the heater are disconnected.

The starter device of the invention has the following main advantages:

-   -   reduced polluting emissions because less fuel is used,    -   faster starting (and preheating),    -   fewer combustion failures,    -   reduced instability, and consequential noise, after starting,    -   simplified engine cylinder head, and    -   application to engines with a low compression ratio.

Furthermore, as already explained hereinabove, the inlet air preheatingmeans do not require more electrical power than a system usingglowplugs.

The invention finds a general application to internal combustion enginesand very specifically to automobile vehicle diesel engines.

1. Method of starting without glowplugs a diesel engine includingcylinders and pistons defining combustion chambers into which areadmitted gases intended to participate in combustion, in which method astrategy is adopted whereby the gases present in the chambers are heatedto a minimum temperature throughout the volume defined by the chamberswhen the pistons are in or near the maximum compression position. 2.Method according to claim 1, wherein said minimum temperature isapproximately 415° C.
 3. Method according to claim 1 wherein said engineincluding a crankshaft (18), an electrical machine (22) is coupled tothe crankshaft to drive it in rotation at a chosen rotation speed thatis higher than a normal rotation speed and is obtained by saidelectrical machine in order to increase the compression of the airpresent in the cylinders of the engine and consequently the temperaturein the cylinders.
 4. Method according to claim 3, wherein the chosenrotation seed is greater than 200 revolutions per minute.
 5. Methodaccording to claim 4, wherein the chosen rotation seed is greater than300 revolutions per minute.
 6. Method according to claim 1, wherein thetotal reduction ratio between the rotor of the electrical machine (22)and the crankshaft is less than 40:1.
 7. Method according to claim 1,wherein the starter is of the gear type and has between the rotor shaftand the starter pinion an internal reduction gear stage the ratiowhereof being less than 4:1.
 8. Method according to claim 7, wherein theengine ring gear has a number of teeth less than or equal to
 100. 9.Method according to claim 1, wherein the compression ratio of the engineis less than or equal to 16.5:1.
 10. Method according to claim 1,wherein the chambers being supplied with gases intended to participatein combustion via a common pipe, said gases are preheated while flowingin said pipe.
 11. Method according to claim 10, wherein said gases arepreheated and their flowrate is adjusted simultaneously.
 12. Methodaccording to claim 3, wherein the gases intended to participate incombustion are preheated and said electrical machine (22) is operated atsaid chosen rotation speed in a coordinated manner.
 13. Method accordingto claim 10, wherein said gases are preheated before operating saidelectrical machine at said chosen rotation speed.
 14. Method accordingto claim 1, wherein starting conditions are detected, information isdeduced relating to “cold start” conditions or “normal start” conditionsand said strategy is adopted depending on said starting conditions. 15.Method according to claim 3, wherein the electrical machine (22) isoperated at the chosen speed or at the normal speed according to whetherthe “cold start” conditions or the “normal start” conditions,respectively, apply.
 16. Method according to claim 14, wherein thestarting conditions relate to: a temperature difference (DT=T−TE)between the temperature (T) outside the vehicle and the temperature (TE)of the engine cooling water or the temperature (TH) of the enginelubricating oil, and the outside temperature T and define the “coldstart” conditions or the “normal start” conditions according to whetherthat temperature difference (DT) or the temperature (T) are respectivelyless than or greater than a given threshold value (S) or (S′). 17.Starting method according to claim 16, wherein the threshold value (S)is 5° or the threshold value (S′) is 0° C.
 18. Device for startingwithout glowplugs a diesel engine including cylinders and pistonsdefining combustion chambers into which are admitted gases intended toparticipate in combustion, said device including means for heating thegases present in the chambers to a minimum temperature throughout thevolume of the chambers when the pistons are in or near a position ofmaximum compression.
 19. Device according to claim 18 including anelectrical machine (22) adapted to be coupled to the crankshaft (18) ofthe engine to drive it in rotation at a chosen rotation speed that ishigher than a normal rotation speed obtained by said electrical machinein order to increase the compression and the quantity of air admittedinto the cylinders of the engine and consequently the temperature in thecylinders.
 20. Device according to claim 19, wherein said electricalmachine (22) is an electric starter that is adapted to operate at one ormore given electrical voltages and is connected to an electrical circuit(28) adapted to supply power to the starter at a boosted electricalvoltage higher than the given electrical voltage.
 21. Device accordingto claim 19, wherein the electrical circuit (28) includes a primaryvoltage source (42) adapted to deliver a nominal voltage of chosen valueand a boosted voltage source (44) adapted to deliver a voltage higherthan the nominal voltage of the primary voltage source (42).
 22. Deviceaccording to claim 21, wherein the boosted voltage source (44) is abattery.
 23. Device according to claim 21, wherein the primary voltagesource (42) is a battery adapted to deliver a nominal voltage of 12volts and the boosted voltage source (44) is a battery adapted todeliver a nominal voltage of 24 volts.
 24. Device according to claim 22,wherein the boosted voltage source (44) is a supercapacitor.
 25. Deviceaccording to claim 21, wherein the primary voltage source (42) is abattery adapted to deliver a nominal voltage of 12 volts and the boostedvoltage source (44) is a supercapacitor adapted to deliver a voltagehigher than 12 volts.
 26. Device according to claim 21, wherein theelectrical circuit (28) includes a DC-DC converter (50) for charging theboosted voltage source (44) from the primary voltage source (42). 27.Device according to claim 21, wherein the electrical circuit (28)includes an electrical relay (48) adapted to operate the electricstarter (22) from the boosted voltage source (44).
 28. Device accordingto claim 18, wherein said circuit includes a first voltage source fordelivering said given voltage, a second voltage source and switchingmeans for combining said voltage sources to obtain said boosted voltage.29. Device according to claim 18, wherein said circuit includes a singlebattery for producing said given voltage and a DC-DC converter forproducing said boosted voltage.
 30. Device according to claim 20,wherein the starting process includes a first phase in which the starteris supplied with power at a given voltage and a second phase in whichsaid starter is supplied with power at a voltage higher than the givenvoltage.
 31. Device according to claim 30, wherein the change betweenthe first phase and the second phase is effected when the pressure inthe injection manifold exceeds a defined threshold.
 32. Device accordingto claim 30, wherein the change between the first phase and the secondphase is effected when the duration of the first phase exceeds a certaintime.
 33. Device according to claim 32, wherein the duration of thefirst phase is a function of the outside temperature and/or thetemperature of the engine cooling liquid.
 34. Device according to claim33, wherein if the temperature is less than or equal to 20° C. theduration of the first phase is 1 s.
 35. Device according to claim 30,wherein when the starter has a pinion cooperating with a ring gear, thechange between the first phase and the second phase is effected when thepinion has begun its penetration into the teeth of the ring gear. 36.Device according to claim 18, including preheating means (30) that areadapted to preheat the gases intended for combustion, referred to as theinlet air (A), said preheating means being provided in a pipe feedingall the combustion chambers simultaneously.
 37. Device according toclaim 30, wherein the preheating means (30) include at least oneelectrically resistive element (R).
 38. Device according to claim 31,wherein said electrically resistive element (R) is integrated into avalve for adjusting the flowrate of the gases intended to participate incombustion, said valve being provided in said pipe.